1. Field of the Invention
The present invention relates to a method of manufacturing an optical disc, more particularly to a method of manufacturing the optical disc by bonding an upper disc plate and a lower disc plate.
2. Prior Art
Computers have made a dramatic leap forward in processing capacity and processing speed. Particularly, storage density of a storage medium has been dramatically improved. Among storage memories, a so-called storing disc, particularly an optical disc is convenient to be carried and has various uses as a storage memory.
An optical disc is generally structured by a discoid substrate made of a synthetic resin such as polycarbonate. Signal pits as information signals are generally recorded in the disc substrate, and a reflecting film such as aluminum, nickel, etc. are formed on signal pits. A protecting resin layer, such as UV curing resin (a so-called UV resin) is formed on the reflecting film so as to protect the signal pits.
The thickness of the disc substrate is generally 0.6 mm in view of storage of signals, manufacturing limitation and strength of the disc substrate. Accordingly, if two pieces of disc substrates each having 0.6 mm in thickness are bonded by an adhesive, the thickness becomes 1.2 mm that is a standard of a compact disc.
Meanwhile, the inventors of the present invention developed a system (U.S. Pat. No. 5,779,855) which comprises a series of processes including an adhesive spreading step and an adhesive curing step in a method of manufacturing an optical disc.
In the system, there are employed processes for bonding two disc substrates, then irradiating the adhesive with UV to cure the adhesive in a state where they are pressed by UV transmittance plates from the upper and lower sides thereof.
In the system, two disc substrates are irradiated with UV and an adhesive is cured while the substrates are moved by a belt conveyer in a curing unit in a state where they are placed on a base table.
After the two disc substrates are passed away from the curing unit, the UV transmittance plates are taken out and bypassed from a main stream of process, then the two disc substrates are delivered to a bonding unit by another belt conveyer.
The base table from which the UV transmittance plates are taken out are fed to the bonding unit by a belt conveyer and two new disc substrates are placed on the base table.
The UV transmittance plates which were taken out from the base table and bypassed from the mainstream are placed on the two new disc substrates. The two new disc substrates are fed to the curing unit, and these operations are repeated.
According to the system set forth above, two disc substrates are placed on the base table and moved by the belt conveyer so that the two disc substrates become unstable in motion.
Particularly, since the two disc substrates are irradiated with UV while they are moved in the curing unit by the belt conveyer in a state where they are placed on the base table, the irradiation time becomes long and the two disc substrates are susceptible to heating by a light source incorporated into the curing unit. Further, since the UV transmittance plates in addition to the base table are moved by the belt conveyer, the conveying or delivering part occupies a large space in the system which is inefficient in view of consumption of energy.